In a CDMA mobile communication system, the power control will directly influence the communication performance of the system, which is mainly characterized in communication capacity and call drop rate.
The method of controlling the forward power of a terminal in a sector in a CDMA mobile communication system usually includes open loop, closed loop, and outer loop control, wherein a control range of the terminal forward transmission power, i.e. the control threshold range of the forward transmission power Ptx_lower and Ptx_upper, needs to be set in the closed loop control, and the actual forward transmission power is confined within the range of these two power thresholds. Ptx_lower is the lower bound of the forward transmission power; if it is too low, call drop will easily happen, especially in fast fading areas, and if it is too high, the capacity of system will be affected. Ptx_upper is the upper bound of forward transmission power; if it is too low, the voice quality can not be ensured in places with bad signal quality, and meanwhile call drop happens easily, and if it is too high, the capacity of system will also be affected, resulting in an overload of the forward transmission power easily. Therefore, determining a suitable upper bound and lower bound of the control threshold of the forward transmission power is important for promoting the performance of a CDMA mobile communication system.
Usually, in a system (or in a sector), Ptx_lower and Ptx_upper are fixed, and are experiential values under theoretical instructions. Due to the particular complexity of mobile communication, the transmission power of a base station is sometimes required to be low, and some other times to be high. As a result, the range of the forward transmission power that is required in practice is fluctuant. The fixed Ptx_lower and Ptx_upper can not adapt to the variation of communication environment varying dynamically and the fluctuation of call capacity, and can not trace this variation in real-time.
In an environment with a complex terrain, there are many shadow areas with small range. When a terminal in a sector gets into a shadow area, if the forward transmission power can not be increased accordingly, the voice quality usually becomes bad due to a sudden deterioration of forward signals, and the threshold of a forward frame error counter maintained by the terminal may even be triggered, which will result in a call drop. Since the mobile station maintains a forward frame error counter, the link will be released and a call drop will occur if the counter exceeds a certain threshold. At this moment, if the upper bound of the forward transmission power is promoted properly to enable the forward transmission power of the mobile station to increase, triggering of the counter will be postponed while the voice quality will be enhanced, and it can be ensured that the forward frame error counter will not exceed the released established threshold value before the mobile station departs from the shadow area.
Additionally, since a process is needed when the terminal implements forward pilot search and soft handoff, if the processing time of searching handoff pilot and/or implementing the soft handoff is too long, in a case that the forward transmission power can not be promoted properly, strong pilot interference will easily lead to a bad forward link quality, and may also lead to a result that the forward signaling can not be demodulated and finally a call drop occurs.
Currently, there are some methods for dynamically adjusting and controlling the forward power of a CDMA mobile communication system, such as the method of channel adaptive power control. This method uses a group of different TPC algorithms (TPCAs) of any size, and the transmission power can be controlled in an adaptive way of channels. Each TPCA should adapt well to a particular type of channels. In this method, it is required to establish different algorithms and rules for determining whether an algorithm is good. However, the use of different algorithms for tracing channels can not ensure the feature of real-time.
To summarize all above, how to optimize the control effect of forward transmission power of the terminal in a CDMA mobile communication system and promote the communication quality of the system is an important technique problem that needs to be solved by the skilled in the art.